Short-Range Wireless Systems
Short-range wireless systems have a typical range of one hundred meters or less. They often combine with systems wired to the Internet to provide communication over long distances. The category of short-range wireless systems includes wireless personal area networks (PANs) and wireless local area networks (LANs). They have the common feature of operating in unlicensed portions of the radio spectrum, usually either in the 2.4 GHz Industrial, Scientific, and Medical (ISM) band or the 5 GHz Unlicensed-National Information Infrastructure (U-NII) band. Wireless personal area networks use low cost, low power wireless devices that have a typical range of ten meters. The best-known example of wireless personal area network technology is the Bluetooth Standard, which operates in the 2.4 GHz ISM band. It provides a peak air link speed of one Mbps and a power consumption low enough for use in personal, portable electronics such as PDAs and mobile phones. Wireless local area networks (LANs) generally operate at higher peak speeds of between 10 to 100 Mbps and have a longer range, which requires greater power consumption. Wireless local area networks are typically used as wireless links from portable laptop computers to a wired LAN, via an access point (AP). Examples of wireless local area network technology include the IEEE 802.11 Wireless LAN Standard and the HIPERLAN Standard, which operates in the 5 GHz U-NII band.
The Bluetooth Short-Range Wireless Technology
Bluetooth is a short-range radio network, originally intended as a cable replacement. It can be used to create networks of up to eight devices operating together. The Bluetooth Special Interest Group, Specification of the Bluetooth System, Volumes 1 and 2, Core and Profiles: Version 1.1, Feb. 22, 2001, describes the principles of Bluetooth device operation and communication protocols. The devices operate in the 2.4 GHz radio band reserved for general use by Industrial, Scientific, and Medical (ISM) applications. Bluetooth devices are designed to find other Bluetooth devices within their ten-meter radio communications range and to discover what services they offer, using a service discovery protocol (SDP).
The SDP searching function relies on links being established between the requesting Bluetooth device, such as a stationary access point device, and the responding Bluetooth device, such as a mobile user's device. When the mobile user's device enters within communicating range of the access point, its Link Controller layer in its transport protocol group handles the exchange of inquiry and paging packets to establish the initial link with the access point device. Then the Logical Link Control and Adaptation Protocol (L2CAP) layer in the transport protocol group passes the link status up to the layers in the middleware protocol group. The SDP searching function in the middleware protocol group can then be used to find out about application programs in the responding Bluetooth device that may provide desired services.
Bluetooth usage models are formally specified in application profiles set forth in the Specification of the Bluetooth System, referred to above. There are 13 application profiles described in Version 1.1 of the specification, including the Generic Access Profile (GAP), Service Discovery Profile (SDP), Generic Object Exchange Profile (GOEP), and Object Push Profile. The Generic Access Profile (GAP) defines how two Bluetooth units discover and establish a connection with each other. The service discovery protocol (SDP) defines the investigation of services available to a Bluetooth unit from other units. Generic Object Exchange Profile (GOEP) describes defines the set of protocols and procedures used by applications in handling object exchanges, e.g. File Transfer Synchronization using the Object Exchange (OBEX) Standard. The OBEX Standard is specified by the Infrared Data Association (IrDA), Object Exchange Protocol, Version 1.2. The OBEX Standard was adopted by Bluetooth as a session-oriented protocol, which allows multiple request/response exchanges in one session as a binary HTTP protocol. The Bluetooth Object Push Profile specification discusses the application of exchanging virtual business cards using the OBEX Standard.
The IEEE 802.11 Wireless LAN Standard
The IEEE 802.11 Wireless LAN Standard defines at least two different physical (PHY) specifications and one common medium access control (MAC) specification. The IEEE 802.11(a) Standard is designed for either the 2.4 GHz ISM band or the 5 GHz U-NII band, and uses orthogonal frequency division multiplexing (OFDM) to deliver up to 54 Mbps data rates. The IEEE 802.11(b) Standard is designed for the 2.4 GHz ISM band and uses direct sequence spread spectrum (DSSS) to deliver up to 11 Mbps data rates. The IEEE 802.11 Wireless LAN Standard describes two major components, the mobile station and the fixed access point (AP). IEEE 802.11 networks can be configured where the mobile stations communicate with a fixed access point. IEEE 802.11 also supports distributed activities similar those of the Bluetooth piconets. The IEEE 802.11 standard provides wireless devices with service inquiry features similar to the Bluetooth inquiry and scanning features.
In order for an IEEE 802.11 mobile station to communicate with other stations in a network, it must first find the stations. The process of finding another station is by inquiring. Active inquiry requires the inquiring station to transmit queries and invoke responses from other wireless stations in a network. In an active inquiry, the mobile station will transmit a probe request frame. If there is a network on the same channel that matches the service set identity (SSID) in the probe request frame, a station in that network will respond by sending a probe response frame to the inquiring station. The probe response includes the information necessary for the inquiring station to access a description of the network. The inquiring station will also process any other received probe response and Beacon frames. Once the inquiring station has processed any responses, or has decided there will be no responses, it may change to another channel and repeat the process. At the conclusion of the inquiry, the station has accumulated information about the networks in its vicinity. Once a station has performed an inquiry that results in one or more network descriptions, the station may choose to join one of the networks. The IEEE 802.11 Wireless LAN Standard is published in three parts as IEEE 802.11-1999; IEEE 802.11a-1999; and IEEE 802.11b-1999, which are available from the IEEE, Inc. web site http://grouper.ieee.org/groups/802/11.
High Performance Radio Local Area Network (HIPERLAN)
The HIPERLAN standard provides a wireless LAN with a high data rate of up to 54 Mbps and a medium-range of 50 meters. HIPERLAN wireless LANs provide multimedia distribution with video QoS, reserved spectrum, and good in-building propagation. There are two HIPERLAN standards. HIPERLAN Type 1 is a dynamic, priority driven channel access protocol similar to wireless Ethernet. HIPERLAN Type 2 is reserved channel access protocol similar to a wireless version of ATM. Both HIPERLAN Type 1 and HIPERLAN Type 2 use dedicated spectrum at 5 GHz. HIPERLAN Type 1 uses an advanced channel equalizer to deal with intersymbol interference and signal multipath. HIPERLAN Type 2 avoids these interference problems by using OFDM and a frequency transform function. The HIPERLAN Type 2 specification offers options for bit rates of 6, 16, 36, and 54 Mbps. The physical layer adopts an OFDM multiple carrier scheme using 48 carrier frequencies per OFDM symbol. Each carrier may then be modulated using BPSK, QPSK, 16-QAM, or 64-QAM to provide different data rates. The modulation schemes chosen for the higher bit rates achieve throughput in the range 30–50 Mbps.
The HIPERLAN Type 1 is a dynamic, priority driven channel access protocol that can form networks of wireless devices. HIPERLAN Type 1 networks support distributed activities similar those of the Bluetooth piconets and IEEE 802.11 independent basic service sets (IBSS). The HIPERLAN Type 1 standard provides wireless devices with service inquiry features similar to those of the Bluetooth inquiry and scanning features and the IEEE 802.11 probe request and response features. An overview of the HIPERLAN Type 1 principles of operation is provided in the publication HIPERLAN Type 1 Standard, ETSI ETS 300 652, WA2 December 1997.
HIPERLAN Type 2 is a reserved channel access protocol that forms networks. HIPERLAN Type 2 networks support distributed activities similar those of the HIPERLAN Type 1 networks, Bluetooth piconets and IEEE 802.11 independent basic service sets (IBSS). HIPERLAN Type 2 provides high-speed radio communication with typical data rates from 6 MHz to 54 Mbps. It connects portable devices with broadband networks that are based on IP, ATM and other technologies. Centralized mode is used to operate HIPERLAN Type 2 as an access network via a fixed access point. A central controller (CC) in the fixed access point provides QoS coordinates the access of the mobile stations support. User mobility is supported within the local service area and wide area roaming mobility can also be supported. An overview of the HIPERLAN Type 2 principles of operation is provided in the Broadband Radio Access Networks (BRAN), HIPERLAN Type 2; System Overview, ETSI TR 101 683 VI.I.1 (2000-02) and a more detailed specification of its ad hoc network architecture is described in HIPERLAN Type 2, Data Link Control (DLC) Layer; Part 4, Extension for Home Environment, ETSI TS 101 761-4V1.2.1 (2000-12).